1. Field of the Invention
The present invention relates to a defect inspection apparatus for inspecting an object, such as a wafer and a chip, for defects.
2. Description of the Background Art
Defects include extraneous material adhering to a surface of an object, and a pattern defect of an object. A semiconductor device will be taken as an example of the objects to be inspected in the description below.
FIG. 19 is a schematic block diagram of a background art defect inspection apparatus. As illustrated in FIG. 19, the background art defect inspection apparatus comprises an X-Y stage 101 for placing thereon a wafer 100 to be inspected, an objective lens 102, a Xe lamp 103, a TV camera 104, an A/D converter 105, an image memory 106, and a defect judgement device 107. FIG. 20 is a partially enlarged top plan view of the wafer 100. As illustrated in FIG. 20, the wafer 100 has a plurality of chips 110 arranged in a matrix.
Description is given on a method of inspecting a circuit pattern 111b fabricated into a chip 110b for defects, using the defect inspection apparatus shown in FIG. 19. First, the X-Y stage 101 is moved to position the wafer 100 so that the Xe lamp 103 illuminates the circuit pattern 111b. Next, the Xe lamp 103 directs light onto the circuit pattern 111b. The light reflected from the circuit pattern 111b passes through the objective lens 102 and reaches the TV camera 104. The TV camera 104 detects the reflected light as an image. The A/D converter 105 converts the detected image into a digital signal to input the digital signal as image data DB to the defect judgement device 107.
The image memory 106 has previously inputted image data DA concerning a circuit pattern 111a fabricated into a chip 110a. The defect judgement device 107 receives the image data DA from the image memory 106, and then subtracts the image data DA from the image data DB to determine a difference therebetween. FIG. 21 shows the image data DA, the image data DB, and the difference data DBxe2x88x92DA. The image data DA, DB and the difference data DBxe2x88x92DA are shown in plan view in the upper part of FIG. 21, and a digital value representing brightness as measured along the line L is illustrated in the lower part of FIG. 21. If the circuit pattern 111b has a defect, the defect appears as defect data 112 in the image data DB. When the brightness of the defect data 112 is not less than a predetermined threshold value X1 as a result of the subtraction of the image data DA from the image data DB, the defect judgement device 107 judges that the circuit pattern 111b has a defect in a position corresponding to the defect data 112.
However, such a background art defect inspection apparatus has presented problems to be described below.
First Problem
As described hereinabove, the background art defect inspection apparatus compares the value of the difference data DBxe2x88x92DA provided by subtracting the image data DA from the image data DB with the predetermined threshold value X1 to judge the presence or absence of a defect. A wafer subjected to the CMP process often has different thicknesses depending on locations in the wafer surface. In such a case, the difference in thickness causes a difference in reflected light intensity. Thus, the value of the difference data DBxe2x88x92DA is not zero but is detected as noises in a nondefective location (FIG. 22). It is therefore difficult to determine whether the difference data DBxe2x88x92DA having a value not less than the threshold value X1 results from a defect or noises. The use of a higher threshold value X2 so as not to detect noises makes it impossible to detect the defect data. Additionally, in combination with the decrease in pattern resolution when detected due to performance limitations of optical systems with recent size reduction of semiconductor devices, the background art defect inspection apparatus presents the problem of low defect detection accuracy.
Second Problem
Some defects in a chip are fatal to semiconductor devices, but some are not. This depends on the positions in which the defects occur in a chip. However, the background art defect inspection apparatus detects all defects in the chip independently of the positions in which the defects occur. Hence, the background art defect inspection apparatus is not capable of judging whether or not the detected defects affect a yield in practice. This results in delayed measures against process failures and the production of dust which give rise to defects, accordingly leading to the increase in manufacturing costs.
According to a first aspect of the present invention, a defect inspection apparatus comprises: a light illuminator for directing light onto a surface of an object to be inspected; a data generator for generating illumination light control data for rendering the intensity of light reflected from the surface uniform throughout the surface, based on a distribution of reflectance of the surface for the light; a light intensity controller for controlling the intensity of the light directed from the light illuminator onto the surface, based on the illumination light control data; and an inspector receiving the light reflected from the surface or scattered by the surface and for inspecting the surface for a defect.
Preferably, according to a second aspect of the present invention, in the defect inspection apparatus of the first aspect, the light intensity controller includes: a liquid crystal filter having a filter surface disposed in an optical path between the light illuminator and the surface; and a filter controller for controlling transmittance of the filter surface for the light, based on the illumination light control data.
Preferably, according to a third aspect of the present invention, in the defect inspection apparatus of the second aspect, the liquid crystal filter is a filter capable of non-uniformly controlling the transmittance in the filter surface.
Preferably, according to a fourth aspect of the present invention, in the defect inspection apparatus of any one of the first to third aspects, the object is a wafer having a surface coated with a film.
Preferably, according to a fifth aspect of the present invention, in the defect inspection apparatus of any one of the first to third aspects, the object is a wafer having a plurality of chips arranged in a matrix; the data generator generates the illumination light control data based on the reflectance for each of the chips or for each of dice; and the light intensity controller controls the intensity of the light for each of the chips or for each of the dice.
Preferably, according to a sixth aspect of the present invention, in the defect inspection apparatus of any one of the first to third aspects, the object is a wafer having a plurality of chips arranged in a matrix; the data generator receives classification data concerning the plurality of chips classified into a first group of chips and a second group of chips in accordance with a predicted distribution of the reflectance of a wafer surface of the wafer; the data generator determines a first reflectance of at least one representative first chip included in the first group as the reflectance of the first group of chips, and determines a second reflectance of at least one representative second chip included in the second group as the reflectance of the second group of chips; and the light intensity controller controls the intensity of the light for each of the first and second groups.
Preferably, according to a seventh aspect of the present invention, in the defect inspection apparatus of any one of the first to third aspects, the object is a wafer having a plurality of chips arranged in a matrix; the data generator receives classification data concerning the plurality of chips classified into a first group of chips expected to be more susceptible to defects and a second group of chips expected to be less susceptible to defects; the data generator determines the reflectance for each of the first group of chips or for each of the dice of the first group of chips, and determines the reflectance of at least one representative chip included in the second group as the reflectance of the second group of chips; and the light intensity controller controls the intensity of the light for each of the first group of chips or for each of the dice of the first group of chips, and controls the intensity of the light commonly for the second group of chips based on the reflectance of the at least one representative chip.
Preferably, according to an eighth aspect of the present invention, in the defect inspection apparatus of any one of the first to third aspects, the object is a chip having a plurality of regions into which different types of semiconductor devices are fabricated; the data generator generates the illumination light control data based on the reflectance of each of the regions; and the light intensity controller controls the intensity of the light for each of the regions.
Preferably, according to a ninth aspect of the present invention, in the defect inspection apparatus of any one of the first to third aspects, the object is a chip having a plurality of regions into which different types of semiconductor devices are fabricated; the inspector receives information concerning a fatal region in which the presence of the defect is fatal to the chip and information concerning a critical size of the defect which is fatal to the chip in the form of data; and the inspector detects only the defect occurring in the fatal region and having a size not less than the critical size, based on the data.
The defect inspection apparatus according to the first aspect of the present invention comprises the light intensity controller capable of correcting a difference in light reflectance in the surface to be inspected because of uneven film thicknesses, to suppress the generation of noises, thereby increasing the accuracy of defect detection.
In accordance with the second aspect of the present invention, the liquid crystal filter is higher in controllability and response speed, achieving minuter filter control.
In accordance with the third aspect of the present invention, proper control of the intensity of light directed from the light illuminator onto the surface to be inspected allows the properly uniform intensity of the light reflected from the surface.
In accordance with the fourth aspect of the present invention, the wafer having a surface coated with a film is inspected for defects, particularly extraneous material, with high accuracy.
In accordance with the fifth aspect of the present invention, light intensity control for each chip or for each die increases the accuracy of the defect inspection.
In accordance with the sixth aspect of the present invention, the determination of the reflectance of a reduced number of chips requires shorter time for inspection than the determination of the reflectance of chips or dice on a one-by-one basis.
In accordance with the seventh aspect of the present invention, the inspection of the second group of chips less susceptible to defects is advantageous in that the determination of the reflectance of a reduced number of chips requires shorter time for inspection than the determination of the reflectance of chips or dice on a one-by-one basis. Additionally, the inspection of the first group of chips more susceptible to defects is advantageous in that the determination of the reflectance for each chip or for each die increases the inspection accuracy.
In accordance with the eighth aspect of the present invention, light intensity control for each of the regions increases the accuracy of the defect inspection.
In accordance with the ninth aspect of the present invention, the inspector does not identify a defect occurring in other than the fatal region and a defect occurring in the fatal region and having a size less than the critical size as being defective. This allows the efficient detection of only fatal defects affecting a product yield.
It is therefore an object of the present invention to provide a defect inspection apparatus capable of detecting a defect in an object to be inspected with high accuracy and with efficiency.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.